The percent yield : 79.9%
Further eplanation
Percent yield is the comparison of the amount of product obtained from a reaction with the amount you calculated
General formula:
Percent yield = (Actual yield / theoretical yield )x 100%
An actual yield is the amount of product actually produced by the reaction. A theoretical yield is the amount of product that you calculate from the reaction equation according to the product and reactant coefficients
Reaction
Fe(s)+S(s)⇒FeS(s)
The reaction produces 6.29 g of iron(II) sulfide⇒an actual yield
The maximum amount that can be produced is 7.87 g ⇒ A theoretical yield